In general, flame spray apparatus operated by hot combustion gases for coating a workpiece with metal are well known in the art. For example, U.S. Pat. No. 4,416,421 to Browning (hereinafter referred to as “Browning”) discloses a high velocity flame spray apparatus. The Browning apparatus includes a combustion chamber receiving at one end thereof a supply of pressurized fuel and oxygen. Ignition means, such as a spark plug, is provided to ignite the fuel. Pressurized hot combustion gases resulting from ignition of the fuel are discharged from an outlet of the combustion chamber through a plurality of ports leading to the inlet of a relatively long nozzle having a converging throat. A coating material is fed into the throat of the nozzle along the longitudinal axis of the nozzle.
The plurality of ports conveying the pressurized combustion gases from the combustion chamber to the inlet of the nozzle are radially spaced around and inclined toward the axis of the nozzle so that the hot combustion gases propel the coating material through the nozzle and also melt or at least heat-soften the material. The molten or heat-softened material exits the nozzle at high velocity and is projected onto the surface of a workpiece thereby to provide the workpiece with a coating of the material. Passageways for cooling water are provided around the exterior of the nozzle.
A commercial embodiment of the flame spray apparatus disclosed in the Browning patent includes a combustion head which is provided as a transition piece between the outlet of the combustion chamber and the inlet end of the nozzle. The combustion head defines a counterbore which receives the hot combustion gases from the combustion chamber.
One known problem associated with the combustion head of the Browning flame sprayer is that a floor of the counterbore receiving the hot combustion gases from the combustion chamber cracks and erodes after a short period of use, thus, severely limiting the useful life of the combustion head. Such cracking and erosion occurs due to the development of local hot spots in the counterbore and thermal fatigue of the body of the combustion head adjacent to the counterbore.
U.S. Pat. No. 4,911,363 to Webber (hereinafter referred to as “Webber”) discloses an improved combustion head for use with flame spray apparatus such as those described in the Browning patent. The Webber patent discloses a combustion head that defines a recess in the floor of the counterbore which receives the continuous flow of hot pressurized combustion gases from the combustion chamber of the flame spray apparatus. The depth of the recess being sufficient to redistribute the heat of the combustion gases to prevent local hot spots in the counterbore. The recess is provided to avoid cracking and erosion in the combustion head by reducing thermal fatigue which occurs in cyclic use of the flame spray apparatus. Similar to the Browning device, the Webber combustion head also provides a plurality of inclined passages for transporting the combustion gases from the combustion chamber to the inlet of the nozzle of the flame spray apparatus.
In use, the Webber combustion head is coupled to a combustion chamber wherein an open end of the combustion chamber extends into and is fully inserted into the counterbore of the combustion head engaging the floor of the counterbore.
Additionally, the Webber combustion head defines a plurality of radially spaced recesses or channels extending longitudinally along the length of the outer surface of the combustion head through which water is passed for cooling the combustion head.
One disadvantage associated with the above-identified prior art combustion heads is that the floor of the counterbore, even with the recess therein as disclosed by Webber, includes a substantial mass of material which receives the hot combustion gases from the combustion chamber and is therefore susceptible to cracking due to the expansion and contraction of the combustion head during the heating and cooling thereof. The mass of the floor of the counterbore also adds to the overall mass of the combustion head thereby contributing to the thermal fatigue of the combustion head over the life thereof due to the cyclic operation of flame spray apparatus under high temperatures.
Additionally, combustion gases contacting the floor of the counterbore cause the floor of the counterbore to erode enlarging the inlets of the combustion gas passages adjacent the counterbore resulting in an uneven flow of gases through the gas passages of the combustion head. Thus, the pressure of the combustion gases conveyed through each of the plurality of inclined gas conduits is not constant therebetween. This uneven pressure in the inclined gas conduits causes the coating material entering the nozzle of the apparatus to be pushed towards the side of the throat of the nozzle opposite the inclined gas conduits with the greatest pressure which causes erosion of the throat of the nozzle and shortens the useful life thereof.
Accordingly, the cracking and erosion of the floor of the counterbore present in the above-describe prior art combustion heads limits the useful life of the combustion head and parts associated therewith.
The floor of the counterbore in the above-identified prior art combustion heads also obstructs the flow of combustion gases entering the combustion head thereby increasing the amount of turbulence associated with the combustion gases entering the combustion head. This turbulence increases the occurrence of uneven erosion, cracking and wear of the material of the combustion head. Additionally, uneven pressure in the gas conduits exiting the interior chamber of the combustion head is increased due to the disrupted flow of the combustion gases entering the combustion head. Thus, the presence of the floor of the counterbore reduces the overall life of the above-identified prior art combustion heads.
Another disadvantage of the above-identified prior art combustion heads, is that a seal provided to retain coolant within a housing of the flame spray apparatus and disposed between the housing in which the combustion head is used in assembly therewith and a material feed passage of the combustion head often fails due to overheating under heavy use conditions. Typically, failure of this seal causes a shut down of a coating operation in which the flame spray apparatus is being used so that the seal can be replaced. The Webber combustion head includes coolant channels extending longitudinally along the length of the outer surface of the combustion head through which water is passed for cooling the combustion head. However, the coolant channels disclosed by Webber do not effectively maintain the inlet to the material feed passage and the seal disposed between the material feed passage and the housing of the flame spray apparatus at an operating temperature low enough to avoid the seal from failure due to heat damage under heavy use conditions.
Based on the foregoing, it is the general object of the present invention to provide an improved combustion head and combustion chamber for use with known flame spray apparatus that improves upon, or overcomes the problems and drawbacks associated with prior art combustion heads.